F. Zhou, L.J. Tian, L. Gao, Z.-S. Wu*
CIESC Journal, 2020, Accepted.
Exfoliation of few-layer graphene flakes from graphite is one of important strategies for the scalable synthesis and industrial application of high-quality graphene. However, the efficient exfoliation of graphite to graphene without use of strong oxidants and acids is still a great challenge. Herein, we developed a green and scalable aqueous-based electrochemical cathodic exfoliation approach, in which graphite as negative electrode can be electrochemically charged and expanded in an electrolyte of 6 mol·L-1potassium hydroxide (KOH) under high current density and exfoliated efficiently into few-layer graphene sheets with the aid of sonication. The resultant few-layer graphene sheets with low oxygen content of 1.27%(wt), and extremely low ID/IG ratio of < 0.035， high electrical conductivity of > 200 S/cm. Moreover, such electrochemically exfoliated graphene (EG) nanosheets are readily used to produce highly solution-processable ink (1 mg/mL) in ethanol without the need of any surfactants, allowing for the production of large-area EG microelectrodes for EG based micro-supercapacitors (EG-MSCs). Furthermore, the as-fabricated aqueous EG-MSCs show ultrahigh scan rate of 1000000 mV/s and short time constant of only 24 ms. More importantly, using ionic liquids-based electrolyte of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide with bis(trifluoromethanesulfonyl)imide lithium salt (EMIMTFSI/LiTFSI), EG-MSCs can work at a high voltage of 4.0 V, and show high volumetric energy density of 113 mW·h·cm-3, outperforming the most reported MSCs (<50 mW·h·cm-3).